Seat post stiffness: Compact frame geometry

[SteveT]

This subject has probably already been discussed here, but I can't find
the specific info I'm looking for, so I thought I'd give it a try
anyway.

I've been using a Dura Ace aluminum seatpost (27.2 x 270 mm) on a
custom-made steel frame with compact-geometry and I've always noticed a
little bit of seatpost flex that can be a bit annoying at times. I have
the Dura Ace post extended just shy of the "max' allowable line. Even
though the seat post flex ends up providing a nice plush ride, I'm
thinking of switching over to a graphite post that's been designed more
towards a compact frame geometry, like a 350 mm Ritchey carbon post.
Any opinions on graphite posts or opinions on relative seat post
stiffness? Hate to change seatposts and find out the new one is no
stiffer than the old one. Now I understand why 31.6 mm seatpost are
becoming more common.

Thanks,
Steve T

 

[Michael Warner]

On 23 Dec 2006 23:38:11 -0800, SteveT wrote:

> Any opinions on graphite posts

Wear disposable latex gloves when you handle them, or they'll
smudge your hands. They're like giant 5B art pencils.

--
Home page: http://members.westnet.com.au/mvw

 

[Qui si parla Campagnolo]

SteveT wrote:
> This subject has probably already been discussed here, but I can't find
> the specific info I'm looking for, so I thought I'd give it a try
> anyway.
>
> I've been using a Dura Ace aluminum seatpost (27.2 x 270 mm) on a
> custom-made steel frame with compact-geometry and I've always noticed a
> little bit of seatpost flex that can be a bit annoying at times. I have
> the Dura Ace post extended just shy of the "max' allowable line. Even
> though the seat post flex ends up providing a nice plush ride, I'm
> thinking of switching over to a graphite post that's been designed more
> towards a compact frame geometry, like a 350 mm Ritchey carbon post.
> Any opinions on graphite posts or opinions on relative seat post
> stiffness? Hate to change seatposts and find out the new one is no
> stiffer than the old one. Now I understand why 31.6 mm seatpost are
> becoming more common.
>
> Thanks,
> Steve T

I really doubt you are feeling that tube of aluminum flex. If it were,
it would eventually break. Perhaps the saddle rails, but not that tube
of 250mm of aluminum.

 

[Ron Ruff]

SteveT wrote:
> Any opinions on graphite posts or opinions on relative seat post
> stiffness? Hate to change seatposts and find out the new one is no
> stiffer than the old one. Now I understand why 31.6 mm seatpost are
> becoming more common.

Larger diameter allows it to be *stronger* and still light. I did some
calculations awhile back and concluded that a very long post (like
400mm) could flex enough that a sensitive person might notice it, but
compared to flex in the saddle it is still very small. I doubt that you
are perceiving flex in that post.

Carbon posts tend to be more flexible than aluminum posts. If you want
to try a stiffer post I'd look at heavy duty aluminum ones with a thick
wall.

 

[Mike Krueger]

SteveT wrote:

> I've been using a Dura Ace aluminum seatpost (27.2 x 270 mm) on a
> custom-made steel frame with compact-geometry and I've always noticed a
> little bit of seatpost flex that can be a bit annoying at times. I have
> the Dura Ace post extended just shy of the "max' allowable line. Even
> though the seat post flex ends up providing a nice plush ride, I'm
> thinking of switching over to a graphite post that's been designed more
> towards a compact frame geometry, like a 350 mm Ritchey carbon post.
> Any opinions on graphite posts or opinions on relative seat post
> stiffness? Hate to change seatposts and find out the new one is no
> stiffer than the old one. Now I understand why 31.6 mm seatpost are
> becoming more common.

I switched from the Easton EC-70 carbon post on my Litespeed to their
EA-70 Taperwall aluminum post, which is similar to your Dura Ace post.
I find the bead-blasted aluminum post to be more rigid and durable than
the carbon version, which would slip down in the frame under load.
Nashbar has the 300mm EA-70 posts on blowout right now for $32.99,
which is a fantastic bargain.

 

[Tim McNamara]

In article <[email protected]>,
"SteveT" <[email protected]> wrote:

> This subject has probably already been discussed here, but I can't
> find the specific info I'm looking for, so I thought I'd give it a
> try anyway.
>
> I've been using a Dura Ace aluminum seatpost (27.2 x 270 mm) on a
> custom-made steel frame with compact-geometry and I've always noticed
> a little bit of seatpost flex that can be a bit annoying at times. I
> have the Dura Ace post extended just shy of the "max' allowable line.
> Even though the seat post flex ends up providing a nice plush ride,
> I'm thinking of switching over to a graphite post that's been
> designed more towards a compact frame geometry, like a 350 mm Ritchey
> carbon post. Any opinions on graphite posts or opinions on relative
> seat post stiffness? Hate to change seatposts and find out the new
> one is no stiffer than the old one. Now I understand why 31.6 mm
> seatpost are becoming more common.

Are you certain that it is seat post flex you are feeling and not saddle
flex? How have you determined it is the seatpost flexing?